Monitor unit optimization in stereotactic body radiotherapy for small peripheral non-small cell lung cancer patients.

Bao-Tian Huang,Zhu Lin,Pei-Xian Lin,Jia-Yang Lu,Chuang-Zhen Chen

doi:10.1038/srep18453

Abstract

The increasingly attractive stereotactic body radiotherapy (SBRT) treatment for stage I lung cancer is concomitant with a large amount of monitor units (MU), leading to excessive out-of-field dose and prolonged beam-on time. The study aims to reduce the MU number and shorten the beam-on time by optimizing the planning parameters. Clinically acceptable treatment plans from fourteen patients suffered from peripheral stage I non-small cell lung cancer (NSCLC) were created in the study. Priority for the upper objective of the target (PUOT), strength and Max MU setting in the MU objective function (MUOF) were adjusted respectively to investigate their effect on MU number, organs at risk (OARs) sparing and beam-on time. We found that the planning parameters influenced the MU number in a PUOT, strength and Max MU dependent manner. Combined with high priority for the UOT (HPUOT) and MUOF, the MU number was reduced from 443 ± 25 to 228 ± 22 MU/Gy without compromising the target coverage and OARs sparing. We also found beam-on time was proportional to MU number and it could be shortened from 7.9 ± 0.5 to 4.1 ± 0.4 minutes.

Highlights

The increasingly attractive stereotactic body radiotherapy (SBRT) treatment for stage I lung cancer is concomitant with a large amount of monitor units (MU), leading to excessive out-of-field dose and prolonged beam-on time
Retrospective studies have demonstrated that stereotactic body radiotherapy (SBRT) treatment was effective for medically inoperable early stage non-small cell lung cancer (NSCLC)[1,2,3]
We found that the planning parameters in the optimizer influenced the MU number in a PUOT, strength and max MU dependent manner

Summary

Introduction

The increasingly attractive stereotactic body radiotherapy (SBRT) treatment for stage I lung cancer is concomitant with a large amount of monitor units (MU), leading to excessive out-of-field dose and prolonged beam-on time. Retrospective studies have demonstrated that stereotactic body radiotherapy (SBRT) treatment was effective for medically inoperable early stage non-small cell lung cancer (NSCLC)[1,2,3]. As the dose regimen was usually larger than 25 Gy per fraction in single-fraction SBRT, the excessive monitor units (MU) and prolonged beam-on time has become an issue of concern It was reported the required MU was in the range of 2000–10000 for a fraction dose in excess of 10 Gy13 and the average beam-on time ranged from 5 to 6 minutes in SBRT treatment with 25 Gy per fraction[10,14]. Few researches have investigated the effect of planning parameters on MU number and beam-on time, for SBRT treatment of lung cancer which always involves high dose fractionation.

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